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JP6673174B2 - Silicon carbide semiconductor device and method of manufacturing the same - Google Patents

Silicon carbide semiconductor device and method of manufacturing the same Download PDF

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Publication number
JP6673174B2
JP6673174B2 JP2016240558A JP2016240558A JP6673174B2 JP 6673174 B2 JP6673174 B2 JP 6673174B2 JP 2016240558 A JP2016240558 A JP 2016240558A JP 2016240558 A JP2016240558 A JP 2016240558A JP 6673174 B2 JP6673174 B2 JP 6673174B2
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layer
conductivity type
guard ring
type
forming
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JP2018098324A (en
JP2018098324A5 (en
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竹内　有一
有一 竹内
龍太 鈴木
龍太 鈴木
永岡　達司
達司 永岡
佐智子 青井
佐智子 青井
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Denso Corp
Toyota Motor Corp
Toyota Central R&D Labs Inc
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Denso Corp
Toyota Motor Corp
Toyota Central R&D Labs Inc
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Priority to JP2016240558A priority Critical patent/JP6673174B2/en
Priority to CN201780075779.5A priority patent/CN110050349B/en
Priority to PCT/JP2017/044580 priority patent/WO2018110556A1/en
Publication of JP2018098324A publication Critical patent/JP2018098324A/en
Publication of JP2018098324A5 publication Critical patent/JP2018098324A5/ja
Priority to US16/427,413 priority patent/US11177353B2/en
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Publication of JP6673174B2 publication Critical patent/JP6673174B2/en
Priority to US17/477,168 priority patent/US11769801B2/en
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Description

本発明は、ディープ層およびガードリング層を有する炭化珪素（以下、ＳｉＣという）半導体装置およびその製造方法に関する。   The present invention relates to a silicon carbide (hereinafter referred to as SiC) semiconductor device having a deep layer and a guard ring layer, and a method for manufacturing the same.

従来より、高い電界破壊強度が得られるパワーデバイスの素材としてＳｉＣが注目されている。ＳｉＣのパワーデバイスとしては、例えばＭＯＳＦＥＴやショットキーダイオードなどが提案されている（例えば、特許文献１参照）。   Conventionally, SiC has been attracting attention as a material for power devices capable of obtaining high electric field breakdown strength. As a SiC power device, for example, a MOSFET, a Schottky diode, and the like have been proposed (for example, see Patent Document 1).

ＳｉＣのパワーデバイスでは、ＭＯＳＦＥＴやショットキーダイオード等のパワー素子が形成されるセル部と、セル部の周囲を囲むガードリング部とが備えられる。セル部とガードリング部との間には、これらの間を繋ぐための繋ぎ部が設けられ、繋ぎ部における半導体基板の表面側には例えば電極パッドが備えられる。そして、ガードリング部を含む外周領域において、半導体基板の表面を窪ませた凹部とすることで、基板の厚み方向において、セル部および繋ぎ部が島状に突出したメサ部となるようにしている。   The SiC power device includes a cell portion in which a power element such as a MOSFET or a Schottky diode is formed, and a guard ring portion surrounding the cell portion. A connecting portion is provided between the cell portion and the guard ring portion for connecting them, and for example, an electrode pad is provided on the surface side of the semiconductor substrate in the connecting portion. In the outer peripheral region including the guard ring portion, the surface of the semiconductor substrate is formed as a concave portion so that the cell portion and the connecting portion become mesa portions projecting in an island shape in the thickness direction of the substrate. .

特開２０１１−１０１０３６号公報JP 2011-101036 A

上記の構成のパワーデバイスを有するＳｉＣ半導体装置において、微細化に伴ってセル部のＭＯＳＦＥＴ等に形成されるｐ型ディープ層の間隔が狭くなると、ｐ型ディープ層から延びる空乏層によって実質的な電流経路の断面積が狭くなる。これにより、ＪＦＥＴ抵抗が増大することから、ｎ-型ドリフト層の上に、ｐ型ディープ層と同じもしくはそれよりも深い位置まで、ｎ-型ドリフト層よりも高不純物濃度となるｎ型電流分散層を形成して低抵抗化する必要がある。 In the SiC semiconductor device having the power device having the above-described configuration, when the distance between the p-type deep layers formed in the MOSFET and the like in the cell portion is reduced with miniaturization, the substantial current is reduced by the depletion layer extending from the p-type deep layer. The cross-sectional area of the path is reduced. Thus, since the JFET resistance is increased, n - type on the drift layer, p-type deep layer to the same or deeper than, n - -type a high impurity concentration than the drift layer n-type current spreading It is necessary to lower the resistance by forming a layer.

しかしながら、このようなｎ型電流分散層を形成する場合、ｎ型電流分散層が比較的高濃度であるために、ｐ型ガードリングの間において電界が入り込み易くなり、電界集中による耐圧低下を招く。これに対応するには、ｐ型ガードリング同士の間隔をより狭くし、電界の入り込みを抑制することが考えられる。ところが、フォトリソグラフィの分解能などに起因して、ｐ型ガードリング同士の間隔の縮小化の限界があり、例えば０．５μｍ以下の間隔に縮小化することが難しい。このため、今後のさらなる微細化に対応することができなくなることが懸念される。   However, when such an n-type current distribution layer is formed, since the n-type current distribution layer has a relatively high concentration, an electric field easily enters between the p-type guard rings, resulting in a reduction in withstand voltage due to electric field concentration. . In order to cope with this, it is conceivable to make the distance between the p-type guard rings narrower and suppress the entry of the electric field. However, due to the resolution of photolithography and the like, there is a limit in reducing the interval between the p-type guard rings, and it is difficult to reduce the interval to, for example, 0.5 μm or less. For this reason, there is a concern that it will not be possible to cope with further miniaturization in the future.

本発明は上記点に鑑みて、電流分散層を形成する場合において、電界集中による耐圧低下を抑制できる構造のＳｉＣ半導体装置およびその製造方法を提供することを目的とする。   In view of the above, it is an object of the present invention to provide a SiC semiconductor device having a structure capable of suppressing a decrease in breakdown voltage due to electric field concentration when a current distribution layer is formed, and a method for manufacturing the same.

上記目的を達成するため、請求項１に記載のＳｉＣ半導体装置は、セル部および外周部に、第１または第２導電型の基板（１）と、基板の表面側に形成され、基板よりも低不純物濃度とされた第１導電型のドリフト層（２）と、ドリフト層の上に形成され、ドリフト層よりも高不純物濃度とされた第１導電型の電流分散層（２ａ）と、を備えている。セル部には、電流分散層にストライプ状に形成された第２導電型層（５）と、第２導電型層に電気的に接続された第１電極（９）と、基板の裏面側に電気的に接続された第２電極（１１）と、を有し、第１電極と第２電極との間に電流を流す縦型の半導体素子が備えられている。また、ガードリング部には、電流分散層の表面から形成されていると共にセル部を囲む複数の枠形状とされたライン状の第２導電型のガードリング（２１）が備えられている。そして、ガードリング部においてセル部よりも電流分散層が凹んだ凹部（２０）が形成されることで、基板の厚み方向において、セル部がガードリング部よりも突き出した島状のメサ部が構成され、メサ部と凹部との境界位置からメサ部の外周側に向けて、ドリフト層の表層部に、ガードリングよりも低不純物濃度とされた第２導電型の電界緩和層（４０）が備えられている。   In order to achieve the above object, the SiC semiconductor device according to claim 1 is formed on a substrate (1) of a first or second conductivity type on a cell portion and an outer peripheral portion, on a surface side of the substrate, and is formed on a surface side of the substrate. A first conductivity type drift layer (2) having a low impurity concentration, and a first conductivity type current dispersion layer (2a) formed on the drift layer and having a higher impurity concentration than the drift layer. Have. In the cell portion, a second conductive type layer (5) formed in a stripe shape on the current dispersion layer, a first electrode (9) electrically connected to the second conductive type layer, and a back surface side of the substrate. A vertical semiconductor element having a second electrode (11) that is electrically connected and allowing a current to flow between the first electrode and the second electrode. The guard ring portion is provided with a plurality of frame-shaped second conductivity type guard rings (21) formed from the surface of the current distribution layer and surrounding the cell portion. By forming the concave portion (20) in which the current distribution layer is recessed from the cell portion in the guard ring portion, an island-shaped mesa portion in which the cell portion protrudes from the guard ring portion in the thickness direction of the substrate is formed. A second conductivity type electric field relaxation layer (40) having a lower impurity concentration than that of the guard ring is provided on the surface layer of the drift layer from the boundary between the mesa and the recess toward the outer periphery of the mesa. Have been.

このように、メサ部と凹部との境界位置からメサ部の外周側に向けて、ドリフト層の表層部に、電界緩和用の電界緩和層を形成している。このため、ガードリングの間への電界の入り込みを抑制することができる。これにより、電界集中が緩和され、電界集中による層間絶縁膜の破壊が抑制されて、耐圧低下を抑制することが可能となる。したがって、所望の耐圧を得ることが可能なＳｉＣ半導体装置とすることができる。   Thus, the electric field relaxation layer for electric field relaxation is formed on the surface layer of the drift layer from the boundary position between the mesa portion and the concave portion toward the outer peripheral side of the mesa portion. For this reason, it is possible to suppress the electric field from entering between the guard rings. As a result, the electric field concentration is reduced, the destruction of the interlayer insulating film due to the electric field concentration is suppressed, and the reduction in breakdown voltage can be suppressed. Therefore, a SiC semiconductor device capable of obtaining a desired breakdown voltage can be obtained.

また、請求項４に記載のＳｉＣ半導体装置では、メサ部と凹部との境界位置からメサ部の外周側に向けて、電流分散層内に、電流分散層およびガードリングよりもキャリア濃度が低くされた第１導電型または第２導電型の電界緩和層（５０）が備えられている。   Further, in the SiC semiconductor device according to the fourth aspect, the carrier concentration is lower in the current spreading layer than in the current spreading layer and the guard ring from the boundary position between the mesa portion and the concave portion toward the outer peripheral side of the mesa portion. And a first conductivity type or second conductivity type electric field relaxation layer (50).

このように、ガードリング部において電流分散層内に電界緩和層を形成するようにしている。このような電界緩和層を形成しても、ガードリング間への電界の入り込みを抑制することができる。したがって、請求項１と同様の効果を得ることができる。   Thus, the electric field relaxation layer is formed in the current distribution layer in the guard ring portion. Even if such an electric field relaxation layer is formed, it is possible to suppress the electric field from entering between the guard rings. Therefore, the same effect as the first aspect can be obtained.

なお、上記各手段の括弧内の符号は、後述する実施形態に記載の具体的手段との対応関係の一例を示すものである。   In addition, the code | symbol in parenthesis of each said means shows an example of the correspondence with the concrete means described in embodiment mentioned later.

第１実施形態にかかるＳｉＣ半導体装置の上面レイアウトを模式的に示した図である。FIG. 2 is a diagram schematically illustrating an upper surface layout of the SiC semiconductor device according to the first embodiment. 図１のII−II断面図である。FIG. 2 is a sectional view taken along line II-II of FIG. 1. 第１実施形態にかかるＳｉＣ半導体装置の製造工程を示した断面図である。FIG. 4 is a cross-sectional view illustrating a manufacturing process of the SiC semiconductor device according to the first embodiment. 図３に続くＳｉＣ半導体装置の製造工程を示した断面図である。FIG. 4 is a cross-sectional view showing a manufacturing step of the SiC semiconductor device following FIG. 3. 第２実施形態にかかるＳｉＣ半導体装置の上面レイアウトを模式的に示した図である。FIG. 9 is a diagram schematically illustrating a top layout of the SiC semiconductor device according to the second embodiment. 第３実施形態にかかるＳｉＣ半導体装置の断面図である。It is a sectional view of a SiC semiconductor device concerning a 3rd embodiment. 第３実施形態にかかるＳｉＣ半導体装置の製造工程を示した断面図である。FIG. 13 is a cross-sectional view illustrating a manufacturing process of the SiC semiconductor device according to the third embodiment. 第３実施形態の変形例で説明するＳｉＣ半導体装置の断面図である。FIG. 15 is a cross-sectional view of a SiC semiconductor device described in a modification of the third embodiment.

以下、本発明の実施形態について図に基づいて説明する。なお、以下の各実施形態相互において、互いに同一もしくは均等である部分には、同一符号を付して説明を行う。   Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent are denoted by the same reference numerals and described.

（第１実施形態）
第１実施形態について説明する。ここでは半導体素子で構成されるパワー素子としてトレンチゲート構造の反転型のＭＯＳＦＥＴが形成されたＳｉＣ半導体装置を例に挙げて説明する。 (1st Embodiment)
A first embodiment will be described. Here, a SiC semiconductor device in which an inversion type MOSFET having a trench gate structure is formed as a power element including a semiconductor element will be described as an example.

図１に示すＳｉＣ半導体装置は、トレンチゲート構造のＭＯＳＦＥＴが形成されるセル部と、このセル部を囲む外周部とを有した構成とされている。外周部は、ガードリング部と、ガードリング部よりも内側、つまりセル部とガードリング部との間に配置される繋ぎ部とを有した構成とされている。なお、図１は断面図ではないが、図を見やすくするために部分的にハッチングを示してある。   The SiC semiconductor device shown in FIG. 1 is configured to have a cell portion in which a MOSFET having a trench gate structure is formed, and an outer peripheral portion surrounding the cell portion. The outer peripheral portion has a configuration including a guard ring portion and a connecting portion disposed inside the guard ring portion, that is, between the cell portion and the guard ring portion. Although FIG. 1 is not a cross-sectional view, hatching is partially shown to make the drawing easier to see.

図２に示すように、ＳｉＣ半導体装置は、ＳｉＣからなるｎ+型基板１を用いて形成され、ｎ+型基板１の主表面上にＳｉＣからなるｎ-型ドリフト層２とｎ型電流分散層２ａとｐ型ベース領域３、および、ｎ+型ソース領域４が順にエピタキシャル成長させられている。 As shown in FIG. 2, SiC semiconductor device is formed using the n + -type substrate 1 made of SiC, made of SiC on the main surface of the n + -type substrate 1 n - -type drift layer 2 and the n-type current spreading The layer 2a, the p-type base region 3, and the n + -type source region 4 are epitaxially grown in this order.

ｎ+型基板１は、例えばｎ型不純物濃度が１．０×１０19／ｃｍ3とされ、表面が（０００１）Ｓｉ面とされている。ｎ-型ドリフト層２は、例えばｎ型不純物濃度が０．５〜２．０×１０16／ｃｍ3とされている。ｎ型電流分散層２ａは、ｎ-型ドリフト層２よりもｎ型不純物濃度が高濃度、つまり低抵抗とされており、より広範囲に電流を分散して流すことで、ＪＦＥＴ抵抗を低減する役割を果たす。例えば、ｎ型電流分散層２ａは、例えば８×１０16／ｃｍ3とされ、厚みが０．５μｍとされている。 The n + -type substrate 1 has, for example, an n-type impurity concentration of 1.0 × 10 19 / cm 3 and a (0001) Si surface. The n − -type drift layer 2 has an n-type impurity concentration of, for example, 0.5 to 2.0 × 10 16 / cm 3 . The n-type current spreading layer 2a has a higher n-type impurity concentration, that is, a lower resistance, than the n − -type drift layer 2, and serves to reduce the JFET resistance by dispersing the current over a wider range. Fulfill. For example, the n-type current dispersion layer 2a is, for example, 8 × 10 16 / cm 3 and has a thickness of 0.5 μm.

また、ｐ型ベース領域３は、チャネル領域が形成される部分で、ｐ型不純物濃度が例えば２．０×１０17／ｃｍ3程度とされ、厚みが３００ｎｍで構成されている。ｎ+型ソース領域４は、ｎ-型ドリフト層２よりも高不純物濃度とされ、表層部におけるｎ型不純物濃度が例えば２．５×１０18〜１．０×１０19／ｃｍ3、厚さ０．５μｍ程度で構成されている。 The p-type base region 3 has a p-type impurity concentration of, for example, about 2.0 × 10 17 / cm 3 and a thickness of 300 nm in a portion where a channel region is formed. The n + -type source region 4 has a higher impurity concentration than the n − -type drift layer 2. The n-type impurity concentration in the surface layer portion is, for example, 2.5 × 10 18 to 1.0 × 10 19 / cm 3 , and the thickness is The thickness is about 0.5 μm.

セル部では、ｎ+型基板１の表面側においてｐ型ベース領域３およびｎ+型ソース領域４が残されており、ガードリング部では、これらｎ+型ソース領域４およびｐ型ベース領域３を貫通してｎ型電流分散層２ａに達するように凹部２０が形成されている。このような構造とすることでメサ構造が構成されている。 In the cell portion, a p-type base region 3 and an n + -type source region 4 are left on the surface side of the n + -type substrate 1, and in the guard ring portion, the n + -type source region 4 and the p-type base region 3 are connected. A recess 20 is formed so as to penetrate and reach n-type current distribution layer 2a. With such a structure, a mesa structure is formed.

また、セル部では、ｎ+型ソース領域４やｐ型ベース領域３を貫通してｎ型電流分散層２ａに達するようにｐ型ディープ層５が形成されている。ｐ型ディープ層５は、ｐ型ベース領域３よりもｐ型不純物濃度が高くされている。具体的には、ｐ型ディープ層５は、ｎ型電流分散層２ａに複数本が等間隔に配置され、互いに交点なく離れて配置されたストライプ状のトレンチ５ａの間に備えられ、エピタキシャル成長によるｐ型のエピタキシャル膜によって構成されている。なお、このトレンチ５ａがディープトレンチに相当するものであり、例えば幅が１μｍ以下、アスペクト比が２以上の深さとされている。 In the cell portion, a p-type deep layer 5 is formed so as to penetrate the n + -type source region 4 and the p-type base region 3 and reach the n-type current distribution layer 2a. The p-type deep layer 5 has a higher p-type impurity concentration than the p-type base region 3. Specifically, a plurality of p-type deep layers 5 are arranged at equal intervals in the n-type current distribution layer 2a, and are provided between stripe-shaped trenches 5a which are arranged without intersections. It is constituted by a type epitaxial film. The trench 5a corresponds to a deep trench, and has a depth of, for example, 1 μm or less and an aspect ratio of 2 or more.

例えば、各ｐ型ディープ層５は、ｐ型不純物濃度が例えば１．０×１０17〜１．０×１０19ｃｍ3、幅０．７μｍ、深さ２．０μｍ程度で構成されている。各ｐ型ディープ層５は、最も深い底部の位置がｎ型電流分散層２ａとｎ-型ドリフト層２との境界位置と同じ位置、もしくはそれよりもｐ型ベース領域３側に位置している。すなわち、ｐ型ディープ層５とｎ型電流分散層２ａとが同じ深さ、もしくはｐ型ディープ層５よりもｎ型電流分散層２ａの方が深い位置まで形成されている。ｐ型ディープ層５は、図１に示すようにセル部の一端から他端に渡って形成されている。そして、ｐ型ディープ層５は、後述するトレンチゲート構造と同方向を長手方向として延設され、トレンチゲート構造の両端よりも更にセル部の外側に延設された後述するｐ型繋ぎ層３０とつながっている。 For example, each p-type deep layer 5 has a p-type impurity concentration of, for example, about 1.0 × 10 17 to 1.0 × 10 19 cm 3 , a width of about 0.7 μm, and a depth of about 2.0 μm. Each p-type deep layer 5 has the deepest bottom located at the same position as the boundary between the n-type current spreading layer 2a and the n − -type drift layer 2, or on the p-type base region 3 side. . That is, the p-type deep layer 5 and the n-type current spreading layer 2 a are formed to the same depth, or to a position where the n-type current spreading layer 2 a is deeper than the p-type deep layer 5. The p-type deep layer 5 is formed from one end to the other end of the cell portion as shown in FIG. The p-type deep layer 5 extends in the longitudinal direction in the same direction as a trench gate structure described later, and a p-type connecting layer 30 described later extends further outside the cell portion than both ends of the trench gate structure. linked.

ｐ型ディープ層５の延設方向については任意であるが、＜１１−２０＞方向に延設し、トレンチ５ａのうち長辺を構成している対向する両壁面が同じ（１−１００）面となるようにすると、埋込エピ時の成長が両壁面で等しくなる。このため、均一な膜質にできると共に、埋込み不良の抑制効果も得られる。   The direction in which the p-type deep layer 5 extends is arbitrary, but extends in the <11-20> direction, and both opposing wall surfaces forming the long side of the trench 5a have the same (1-100) plane. Then, the growth at the time of the burying epi becomes equal on both wall surfaces. For this reason, uniform film quality can be obtained, and an effect of suppressing poor embedding can be obtained.

また、ｐ型ベース領域３およびｎ+型ソース領域４を貫通してｎ-型ドリフト層２に達するように、例えば幅が０．８μｍ、深さが１．０μｍのゲートトレンチ６が形成されている。このゲートトレンチ６の側面と接するように上述したｐ型ベース領域３およびｎ+型ソース領域４が配置されている。ゲートトレンチ６は、図２の紙面左右方向を幅方向、紙面垂直方向を長手方向、紙面上下方向を深さ方向とするライン状のレイアウトで形成されている。また、図１に示すように、ゲートトレンチ６は、複数本がそれぞれｐ型ディープ層５の間に挟まれるように配置され、それぞれが平行に等間隔で並べられることでストライプ状とされている。 A gate trench 6 having a width of, for example, 0.8 μm and a depth of 1.0 μm is formed to penetrate the p-type base region 3 and the n + -type source region 4 to reach the n − -type drift layer 2. I have. The above-described p-type base region 3 and n + -type source region 4 are arranged so as to be in contact with the side surface of gate trench 6. The gate trenches 6 are formed in a line layout in which the width direction is the horizontal direction in FIG. 2, the longitudinal direction is the vertical direction in the drawing, and the depth direction is the vertical direction in the drawing. Further, as shown in FIG. 1, a plurality of gate trenches 6 are arranged so as to be sandwiched between the p-type deep layers 5, respectively, and are arranged in parallel at equal intervals to form a stripe shape. .

さらに、ｐ型ベース領域３のうちゲートトレンチ６の側面に位置している部分を、縦型ＭＯＳＦＥＴの作動時にｎ+型ソース領域４とｎ-型ドリフト層２との間を繋ぐチャネル領域として、チャネル領域を含むゲートトレンチ６の内壁面にはゲート絶縁膜７が形成されている。そして、ゲート絶縁膜７の表面にはドープドＰｏｌｙ−Ｓｉにて構成されたゲート電極８が形成されており、これらゲート絶縁膜７およびゲート電極８によってゲートトレンチ６内が埋め尽くされている。 Further, a portion of the p-type base region 3 located on the side surface of the gate trench 6 is used as a channel region connecting the n + -type source region 4 and the n − -type drift layer 2 when the vertical MOSFET operates. A gate insulating film 7 is formed on the inner wall surface of the gate trench 6 including the channel region. A gate electrode 8 made of doped Poly-Si is formed on the surface of the gate insulating film 7, and the gate trench 6 is completely filled with the gate insulating film 7 and the gate electrode 8.

また、ｎ+型ソース領域４およびｐ型ディープ層５の表面やゲート電極８の表面には、層間絶縁膜１０を介して第１電極に相当するソース電極９や電極パッド部に配置されたゲートパッド３１が形成されている。ソース電極９およびゲートパッド３１は、複数の金属、例えばＮｉ／Ａｌ等にて構成されている。そして、複数の金属のうち少なくともｎ型ＳｉＣ、具体的にはｎ+型ソース領域４やｎ型ドープの場合のゲート電極８と接触する部分はｎ型ＳｉＣとオーミック接触可能な金属で構成されている。また、複数の金属のうち少なくともｐ型ＳｉＣ、具体的にはｐ型ディープ層５と接触する部分はｐ型ＳｉＣとオーミック接触可能な金属で構成されている。なお、これらソース電極９およびゲートパッド３１は、層間絶縁膜１０上に形成されることで電気的に絶縁されている。そして、層間絶縁膜１０に形成されたコンタクトホールを通じて、ソース電極９はｎ+型ソース領域４およびｐ型ディープ層５と電気的に接触させられ、ゲートパッド３１はゲート電極８と電気的に接触させられている。 Further, on the surface of the n + type source region 4 and the p type deep layer 5 and the surface of the gate electrode 8, the gate electrode disposed on the source electrode 9 corresponding to the first electrode or the electrode pad portion via the interlayer insulating film 10. A pad 31 is formed. The source electrode 9 and the gate pad 31 are made of a plurality of metals, for example, Ni / Al or the like. At least a portion of the plurality of metals that is in contact with the n-type SiC, specifically, the n + -type source region 4 or a portion that is in contact with the gate electrode 8 in the case of n-type doping is made of a metal capable of ohmic contact with the n-type SiC. I have. At least a portion of the plurality of metals that is in contact with the p-type SiC, specifically, a portion that is in contact with the p-type deep layer 5 is made of a metal that can make ohmic contact with the p-type SiC. The source electrode 9 and the gate pad 31 are formed on the interlayer insulating film 10 to be electrically insulated. Source electrode 9 is electrically contacted with n + type source region 4 and p type deep layer 5 through a contact hole formed in interlayer insulating film 10, and gate pad 31 is electrically contacted with gate electrode 8. Have been allowed.

さらに、ｎ+型基板１の裏面側にはｎ+型基板１と電気的に接続された第２電極に相当するドレイン電極１１が形成されている。このような構造により、ｎチャネルタイプの反転型のトレンチゲート構造のＭＯＳＦＥＴが構成されている。そして、このようなＭＯＳＦＥＴが複数セル配置されることでセル部が構成されている。 Further, on the back side of the n + -type substrate 1 the drain electrode 11 corresponding to the second electrode electrically connected to the n + -type substrate 1 is formed. With such a structure, an n-channel MOSFET having an inverted trench gate structure is formed. A cell section is configured by arranging a plurality of such MOSFETs.

一方、ガードリング部では、上記したように、ｎ+型ソース領域４およびｐ型ベース領域３を貫通してｎ型電流分散層２ａに達するように凹部２０が形成されている。このため、セル部から離れた位置ではｎ+型ソース領域４およびｐ型ベース領域３が除去されて、ｎ型電流分散層２ａが露出させられている。そして、ｎ+型ＳｉＣ基板１の厚み方向において、凹部２０よりも内側に位置するセル部や繋ぎ部が島状に突き出したメサ部となっている。 On the other hand, in the guard ring portion, as described above, recess 20 is formed so as to penetrate n + -type source region 4 and p-type base region 3 to reach n-type current distribution layer 2a. Therefore, at a position away from the cell portion, the n + -type source region 4 and the p-type base region 3 are removed, so that the n-type current distribution layer 2a is exposed. Then, in the thickness direction of the n + -type SiC substrate 1, the cell portion and the connecting portion located inside the recess 20 are mesa portions protruding in an island shape.

また、凹部２０の下方に位置するｎ型電流分散層２ａの表層部には、セル部を囲むように、図１中では７本記載してあるが、複数本のｐ型ガードリング２１が備えられている。本実施形態の場合、ｐ型ガードリング２１を四隅が丸められた四角形状としているが、円形状など他の枠形状で構成されていても良い。ｐ型ガードリング２１は、ｎ型電流分散層２ａに形成されたトレンチ２１ａ内に配置され、エピタキシャル成長によるｐ型のエピタキシャル膜によって構成されている。なお、このトレンチ２１ａがガードリングトレンチに相当するものであり、例えば幅が１μｍ以下、アスペクト比が２以上の深さとされている。   In the surface layer portion of the n-type current distribution layer 2a located below the concave portion 20, seven p-type guard rings 21 are provided in FIG. 1 so as to surround the cell portion. Have been. In the case of the present embodiment, the p-type guard ring 21 has a square shape with rounded four corners, but may have another frame shape such as a circular shape. The p-type guard ring 21 is arranged in a trench 21a formed in the n-type current distribution layer 2a, and is made of a p-type epitaxial film formed by epitaxial growth. The trench 21a corresponds to a guard ring trench, and has a width of 1 μm or less and an aspect ratio of 2 or more, for example.

ｐ型ガードリング２１を構成する各部は、上記したｐ型ディープ層５と同様の構成とされている。ｐ型ガードリング２１は、上面形状がセル部および繋ぎ部を囲む枠形状のライン状とされている点において、直線状に形成されたｐ型ディープ層５と異なっているが、他は同様である。すなわち、ｐ型ガードリング２１はｐ型ディープ層５と同様の幅、同様の厚さ、つまり同様の深さとされている。また、各ｐ型ガードリング２１の間隔については、等間隔であっても良いが、より内周側、つまりセル部側において電界集中を緩和して等電位線がより外周側に向かうように、ｐ型ガードリング２１の間隔がセル部側で狭く外周側に向かうほど大きくされている。   Each part configuring the p-type guard ring 21 has the same configuration as the p-type deep layer 5 described above. The p-type guard ring 21 is different from the p-type deep layer 5 formed linearly in that the upper surface has a frame-shaped line shape surrounding the cell portion and the connecting portion, but is otherwise the same. is there. That is, the p-type guard ring 21 has the same width and the same thickness as the p-type deep layer 5, that is, the same depth. In addition, the intervals between the p-type guard rings 21 may be equal, but the electric field concentration is relaxed on the inner peripheral side, that is, on the cell side, so that the equipotential lines are directed to the outer peripheral side. The interval between the p-type guard rings 21 is narrow on the cell portion side and is increased toward the outer peripheral side.

なお、図示していないが、必要に応じてｐ型ガードリング２１よりも外周にＥＱＲ構造が備えられることにより、セル部を囲む外周耐圧構造が備えられたガードリング部が構成されている。   Although not shown, an EQR structure is provided on the outer periphery of the p-type guard ring 21 as necessary, so that a guard ring portion provided with an outer peripheral pressure resistant structure surrounding the cell portion is formed.

さらに、セル部からガードリング部に至るまでの間を繋ぎ部として、繋ぎ部において、ｎ-型ドリフト層２の表層部に複数本のｐ型繋ぎ層３０が形成されている。本実施形態の場合、図１中の破線ハッチングに示すように、セル部を囲むように繋ぎ部が形成されており、さらに繋ぎ部の外側を囲むように、四隅が丸められた四角形状のｐ型ガードリング２１が複数本形成されている。ｐ型繋ぎ層３０は、セル部に形成されるｐ型ディープ層５と平行に複数本並べて配置されており、本実施形態では、隣り合うｐ型ディープ層５同士の間の間隔と等間隔に配置されている。また、セル部からｐ型ガードリング２１までの距離が離れている場所では、ｐ型ディープ層５からｐ型繋ぎ層３０を延設しており、ｐ型繋ぎ層３０の先端からｐ型ガードリング２１までの距離が短くなるようにしている。 Furthermore, a plurality of p-type connecting layers 30 are formed in the surface layer of the n − -type drift layer 2 at the connecting portion, with the region from the cell portion to the guard ring portion as the connecting portion. In the case of the present embodiment, as shown by the dashed hatching in FIG. 1, a connecting portion is formed so as to surround the cell portion, and further, a square p having four rounded corners is formed so as to surround the outside of the connecting portion. A plurality of mold guard rings 21 are formed. A plurality of the p-type connecting layers 30 are arranged in parallel with the p-type deep layer 5 formed in the cell portion. In the present embodiment, the p-type connecting layers 30 are arranged at equal intervals between adjacent p-type deep layers 5. Are located. In a place where the distance from the cell portion to the p-type guard ring 21 is large, the p-type connecting layer 30 extends from the p-type deep layer 5, and the p-type guard ring extends from the tip of the p-type connecting layer 30. The distance to 21 is shortened.

各ｐ型繋ぎ層３０は、ｎ+型ソース領域４およびｐ型ベース領域３を貫通してｎ型ドリフト層２に達するトレンチ３０ａ内に配置され、エピタキシャル成長によるｐ型のエピタキシャル膜によって構成されている。ｐ型ディープ層５の長手方向におけるセル部とガードリング部との間では、ｐ型繋ぎ層３０がｐ型ディープ層５の先端に繋げられて形成されている。なお、このトレンチ３０ａが繋ぎトレンチに相当するものであり、例えば幅が１μｍ以下、アスペクト比が２以上の深さとされている。ｐ型繋ぎ層３０は、ｐ型ベース領域３に接触させられていることから、ソース電位に固定される。 Each p-type connecting layer 30 is arranged in a trench 30a that reaches the n-type drift layer 2 through the n + -type source region 4 and the p-type base region 3, and is formed by a p-type epitaxial film formed by epitaxial growth. . Between the cell portion and the guard ring portion in the longitudinal direction of the p-type deep layer 5, a p-type connecting layer 30 is formed to be connected to the tip of the p-type deep layer 5. The trench 30a corresponds to a connecting trench, and has a width of 1 μm or less and an aspect ratio of 2 or more, for example. Since the p-type connecting layer 30 is in contact with the p-type base region 3, it is fixed at the source potential.

ｐ型繋ぎ層３０を構成する各部は、上記したｐ型ディープ層５やｐ型ガードリング２１と同様の構成とされており、ｐ型繋ぎ層３０の上面形状が直線状とされている点において、枠形状に形成されたｐ型ガードリング２１と異なっているが、他は同様である。すなわち、ｐ型繋ぎ層３０は、ｐ型ディープ層５やｐ型ガードリング２１と同様の幅、同様の厚さ、つまり同様の深さとされている。また、各ｐ型繋ぎ層３０の間隔については、本実施形態ではセル部におけるｐ型ディープ層５同士の間隔と等間隔とされているが、異なる間隔であっても良い。   Each part constituting the p-type connecting layer 30 has the same configuration as the above-described p-type deep layer 5 and p-type guard ring 21, and is different in that the upper surface shape of the p-type connecting layer 30 is linear. , A p-type guard ring 21 formed in a frame shape, but otherwise the same. That is, the p-type connecting layer 30 has the same width and the same thickness as the p-type deep layer 5 and the p-type guard ring 21, that is, the same depth. Further, in the present embodiment, the spacing between the p-type connecting layers 30 is equal to the spacing between the p-type deep layers 5 in the cell portion, but may be different.

このようなｐ型繋ぎ層３０を形成し、かつ、ｐ型繋ぎ層３０同士の間を所定間隔、例えばｐ型ディープ層５と等間隔もしくはそれ以下に設定することで、ｐ型繋ぎ層３０の間において等電位線が過剰にせり上がることを抑制できる。これにより、ｐ型繋ぎ層３０の間において電界集中が発生する部位が形成されることを抑制でき、耐圧低下を抑制することが可能となる。   By forming such a p-type tie layer 30 and setting the distance between the p-type tie layers 30 to a predetermined distance, for example, equal to or less than the p-type deep layer 5, the p-type tie layer 30 Excessive rise of the equipotential lines between them can be suppressed. Thereby, it is possible to suppress the formation of the portion where the electric field concentration occurs between the p-type connecting layers 30, and it is possible to suppress the decrease in the withstand voltage.

なお、各ｐ型繋ぎ層３０における長手方向の両端、つまりトレンチ３０ａの両端では、ｐ型繋ぎ層３０の上面形状が半円形とされている。トレンチ３０ａの両端の上面形状を四角形状にしても良いが、角部にｎ型層が先に形成されることでｎ型化することがある。このため、ｐ型繋ぎ層３０の両端の上面形状を半円形とすることで、ｎ型層が形成される部分を無くすことが可能となる。   At both ends in the longitudinal direction of each p-type connecting layer 30, that is, at both ends of the trench 30a, the top surface of the p-type connecting layer 30 has a semicircular shape. Although the top surface shape at both ends of the trench 30a may be square, the n-type layer may be formed at the corner first to make it n-type. For this reason, by making the top surface shape of both ends of the p-type connecting layer 30 semicircular, it is possible to eliminate the portion where the n-type layer is formed.

また、繋ぎ部においても、ｎ+型ソース領域４の表面に層間絶縁膜１０が形成されている。上記したゲートパッド３１は、繋ぎ部において、層間絶縁膜１０の上に形成されている。 Also in the connecting portion, an interlayer insulating film 10 is formed on the surface of the n + type source region 4. The above-described gate pad 31 is formed on the interlayer insulating film 10 at the connection portion.

このように、セル部とガードリング部との間に繋ぎ部を備えた構造とし、繋ぎ部を幅狭のトレンチ３０ａ内に埋め込まれた複数本のｐ型繋ぎ層３０によって構成している。このため、仮にトレンチ３０ａを幅広のもので形成する場合には、トレンチ３０ａ内を埋め込むことができないためにｐ型繋ぎ層３０の厚みが薄くなったり、ｐ型繋ぎ層３０をエッチバックして平坦化する際に部分的にｐ型繋ぎ層３０が無くなることがある。しかしながら、このようにトレンチ３０ａを幅狭のもので構成しているため、トレンチ３０ａ内に的確に埋め込まれ、ｐ型繋ぎ層３０の厚みが薄くなったり、ｐ型繋ぎ層３０が部分的に無くなってしまうことを抑制することが可能となる。その反面、ｐ型繋ぎ層３０を複数に分割した構造としていることから、ｐ型繋ぎ層３０の間に等電位線がせり上がってくる可能性がある。しかしながら、ｐ型繋ぎ層３０同士の間を所定間隔、例えばｐ型ディープ層５と等間隔もしくはそれ以下とすることで、等電位線の過剰なせり上がりを抑制でき、耐圧低下を抑制できる。   As described above, the structure has a connecting portion between the cell portion and the guard ring portion, and the connecting portion is constituted by the plurality of p-type connecting layers 30 buried in the narrow trenches 30a. For this reason, if the trench 30a is formed to be wide, the inside of the trench 30a cannot be buried, so that the thickness of the p-type connecting layer 30 is reduced, or the p-type connecting layer 30 is etched back to be flat. In some cases, the p-type connecting layer 30 may be partially lost. However, since the trench 30a is formed to have a narrow width, the trench 30a is accurately buried in the trench 30a, the thickness of the p-type connecting layer 30 is reduced, or the p-type connecting layer 30 is partially eliminated. Can be suppressed. On the other hand, since the p-type connecting layer 30 is divided into a plurality of parts, the equipotential lines may rise between the p-type connecting layers 30. However, by setting the interval between the p-type connecting layers 30 to a predetermined interval, for example, the same interval as or less than the p-type deep layer 5, an excessive rise of the equipotential lines can be suppressed, and a decrease in withstand voltage can be suppressed.

さらに、本実施形態では、繋ぎ部からガードリング部に至るようにｎ-型ドリフト層２の表層部に、電界緩和層４０を形成している。電界緩和層４０は、少なくともガードリング部のうちのセル部や繋ぎ部寄りの位置、つまりメサ部と凹部２０との境界位置からメサ部の外周方向に形成されていれば良いが、本実施形態では繋ぎ部のうちのガードリング部寄りの位置にも形成されるようにしてある。より詳しくは、電界緩和層４０は、ガードリング部のうちのセル部や繋ぎ部寄りの位置から繋ぎ部のうちのガードリング部寄りの位置にかけて全域形成されており、少なくともメサ部を囲む帯状の枠体形状とされている。電界緩和層４０のｐ型不純物濃度は、例えば０．５×１０17／ｃｍ3とされており、ｐ型ディープ層５やｐ型ガードリング２１よりも低不純物濃度とされている。電界緩和層４０の厚みについては任意であり、例えば０．５μｍ程度とされる。 Further, in the present embodiment, the electric field relaxation layer 40 is formed on the surface of the n − -type drift layer 2 so as to extend from the connection portion to the guard ring portion. The electric field relaxation layer 40 may be formed at least in the guard ring portion near the cell portion or the connecting portion, that is, in the outer peripheral direction of the mesa portion from the boundary position between the mesa portion and the concave portion 20. In this case, the connecting portion is formed at a position near the guard ring portion. More specifically, the electric field relaxation layer 40 is formed over the entire area from the position near the cell portion or the connecting portion of the guard ring portion to the position near the guard ring portion of the connecting portion, and at least has a band shape surrounding the mesa portion. It has a frame shape. The p-type impurity concentration of the electric field relaxation layer 40 is, for example, 0.5 × 10 17 / cm 3 , which is lower than the p-type deep layer 5 and the p-type guard ring 21. The thickness of the electric field relaxation layer 40 is arbitrary, and is, for example, about 0.5 μm.

上記したように、パワー素子の微細化に伴って、ｐ型ガードリング２１の間隔が狭くなるが、ｎ型電流分散層２ａを形成すると、ＪＦＥＴ抵抗の低減を図ることができる反面、ｐ型ガードリング２１の間に電界が入り込み易くなる。このため、ｐ型ガードリング２１の間の間隔を狭めることで、ｐ型ガードリング２１の間への電界の入り込みを抑制したいが、ｐ型ガードリング２１が配置されるトレンチ２１ａを形成する際のフォトリソグラフィの分解能に伴う縮小化の限界がある。   As described above, with the miniaturization of the power element, the interval between the p-type guard rings 21 is reduced. However, when the n-type current distribution layer 2a is formed, the JFET resistance can be reduced, but the p-type guard ring 21 can be reduced. An electric field easily enters between the rings 21. For this reason, it is desired to suppress the electric field from entering between the p-type guard rings 21 by reducing the interval between the p-type guard rings 21. However, when forming the trench 21 a in which the p-type guard ring 21 is arranged, There is a limit of miniaturization accompanying the resolution of photolithography.

これに対して、電界緩和層４０を形成することで、ｐ型ガードリング２１の間への電界の入り込みを抑制することができる。なお、ガードリング部内における電界緩和層４０の形成範囲については、基本的にはｐ型ガードリング２１の配置間隔やｐ型ガードリング２１とｎ型電流分散層２ａそれぞれの不純物濃度に基づいて決まる。すなわち、ｐ型ガードリング２１は、セル部側において電界集中を緩和して等電位線がより外周側に向かうように形成されるが、その配置間隔やｐ型ガードリング２１およびｎ型電流分散層２ａの不純物濃度によって電界の入り込み方が変わってくる。このため、仮に、電界緩和層４０が形成されていなければ、ｐ型ガードリング２１間への電界が入り込んだときに、その上に形成される層間絶縁膜１０まで達すると想定される位置を含むように、電界緩和層４０を形成している。   On the other hand, by forming the electric field relaxation layer 40, it is possible to suppress the electric field from entering between the p-type guard rings 21. The formation range of the electric field relaxation layer 40 in the guard ring portion is basically determined based on the arrangement interval of the p-type guard rings 21 and the respective impurity concentrations of the p-type guard ring 21 and the n-type current dispersion layer 2a. In other words, the p-type guard ring 21 is formed so that the electric field concentration is eased on the cell portion side so that the equipotential lines are directed to the outer peripheral side. How the electric field enters depends on the impurity concentration of 2a. Therefore, if the electric field relaxation layer 40 is not formed, when an electric field enters between the p-type guard rings 21, it includes a position that is assumed to reach the interlayer insulating film 10 formed thereon. Thus, the electric field relaxation layer 40 is formed.

以上のような構造により、本実施形態にかかるＳｉＣ半導体装置が構成されている。このように構成されるＳｉＣ半導体装置は、ＭＯＳＦＥＴをオンするときには、ゲート電極８への印加電圧を制御することでゲートトレンチ６の側面に位置するｐ型ベース領域３の表面部にチャネル領域を形成する。これにより、ｎ+型ソース領域４およびｎ-型ドリフト層２を介して、ソース電極９およびドレイン電極１１の間に電流を流す。 With the above structure, the SiC semiconductor device according to the present embodiment is configured. In the SiC semiconductor device thus configured, when the MOSFET is turned on, a channel region is formed on the surface of the p-type base region 3 located on the side surface of the gate trench 6 by controlling the voltage applied to the gate electrode 8. I do. Thus, a current flows between the source electrode 9 and the drain electrode 11 via the n + type source region 4 and the n − type drift layer 2.

また、ＭＯＳＦＥＴのオフ時には、高電圧が印加されたとしても、トレンチゲート構造よりも深い位置まで形成されたｐ型ディープ層５によってゲートトレンチ底部への電界の入り込みが抑制されて、ゲートトレンチ底部での電界集中が緩和される。これにより、ゲート絶縁膜７の破壊が防止される。   Further, when the MOSFET is turned off, even if a high voltage is applied, the p-type deep layer 5 formed to a position deeper than the trench gate structure suppresses the entry of an electric field into the bottom of the gate trench. Field concentration is reduced. This prevents the gate insulating film 7 from being broken.

さらに、繋ぎ部では、等電位線のせり上がりが抑制され、ガードリング部側に向かうようにされる。また、ガードリング部において、ｐ型ガードリング２１によって等電位線の間隔が外周方向に向かって広がりながら終端させられるようになり、ガードリング部でも所望の耐圧を得ることができる。   Further, at the connecting portion, the rise of the equipotential lines is suppressed, and the connecting portion is directed to the guard ring portion side. Further, in the guard ring portion, the equipotential lines are terminated by the p-type guard ring 21 while the interval between the equipotential lines is increased toward the outer peripheral direction, so that the guard ring portion can also obtain a desired withstand voltage.

そして、少なくともガードリング部における繋ぎ部側に電界緩和層４０を備えてあるため、ｐ型ガードリング２１の間への電界の入り込みが抑制される。これにより、電界集中が緩和され、電界集中による層間絶縁膜１０の破壊が抑制されて、耐圧低下を抑制することが可能となる。したがって、所望の耐圧を得ることが可能なＳｉＣ半導体装置とすることができる。   Further, since the electric field relaxation layer 40 is provided at least on the connecting portion side of the guard ring portion, entry of an electric field between the p-type guard rings 21 is suppressed. This alleviates the electric field concentration, suppresses the destruction of the interlayer insulating film 10 due to the electric field concentration, and suppresses the reduction in breakdown voltage. Therefore, a SiC semiconductor device capable of obtaining a desired breakdown voltage can be obtained.

続いて、本実施形態に係るＳｉＣ半導体装置の製造方法について図３〜図４を参照して説明する。   Subsequently, a method for manufacturing the SiC semiconductor device according to the present embodiment will be described with reference to FIGS.

〔図３（ａ）に示す工程〕
まず、半導体基板として、ｎ+型基板１を用意する。そして、このｎ+型基板１の主表面上にＳｉＣからなるｎ-型ドリフト層２をエピタキシャル成長させたのち、図示しないマスクを用いて、ｎ-型ドリフト層２の表層部にｐ型不純物をイオン注入すると共に活性化アニールを行うことで電界緩和層４０を形成する。 [Step shown in FIG. 3 (a)]
First, an n + type substrate 1 is prepared as a semiconductor substrate. After an n − -type drift layer 2 made of SiC is epitaxially grown on the main surface of the n + -type substrate 1, p-type impurities are ion-implanted into the surface layer of the n − -type drift layer 2 using a mask (not shown). By implanting and performing activation annealing, the electric field relaxation layer 40 is formed.

なお、電界緩和層４０については、少なくともガードリング部の形成予定位置のうちの繋ぎ部の形成予定位置よりに形成されていれば良いが、ここでは繋ぎ部の形成予定位置内に入り込むように形成するようにしている。   The electric field relaxation layer 40 may be formed at least at a position where the connecting portion is to be formed among the positions where the guard ring portion is to be formed. I am trying to do it.

〔図３（ｂ）に示す工程〕
続いて、マスクを除去したのち、ｎ-型ドリフト層２および電界緩和層４０の上に、ｎ型電流分散層２ａ、ｐ型ベース領域３およびｎ+型ソース領域４を順にエピタキシャル成長させる。 [Step shown in FIG. 3B]
Subsequently, after removing the mask, an n-type current distribution layer 2a, a p-type base region 3 and an n + -type source region 4 are epitaxially grown on the n − -type drift layer 2 and the electric field relaxation layer 40 in this order.

〔図３（ｃ）に示す工程〕
次に、ｎ+型ソース領域４の表面に図示しないマスクを配置し、マスクのうちのｐ型ディープ層５、ｐ型ガードリング２１およびｐ型繋ぎ層３０の形成予定領域を開口させる。そして、マスクを用いてＲＩＥ（Reactive Ion Etching）などの異方性エッチングを行うことにより、トレンチ５ａ、２１ａ、３０ａを形成する。 [Step shown in FIG. 3 (c)]
Next, a mask (not shown) is arranged on the surface of the n + -type source region 4, and a region where the p-type deep layer 5, the p-type guard ring 21 and the p-type connecting layer 30 are to be formed is opened. Then, the trenches 5a, 21a, and 30a are formed by performing anisotropic etching such as RIE (Reactive Ion Etching) using a mask.

このとき、上記したように、電界緩和層４０を、ガードリング部の形成予定位置のうちのセル部や繋ぎ部の形成予定位置寄りに加えて、繋ぎ部の形成予定位置のうちガードリング部の形成予定位置寄りにも形成している。このため、マスクずれによってトレンチ５ａ、２１ａ、３０ａの形成位置がずれたとしても、少なくともガードリング部のうち電界緩和層４０を形成しておきたい位置には、的確に電界緩和層４０が配置されるようにすることができる。また、電界緩和層４０を帯状の枠体形状で形成できることから、微細加工を行う必要なく、容易に形成することができる。   At this time, as described above, the electric field relaxation layer 40 is added to the guard ring portion in the planned formation position of the guard ring portion in addition to the cell portion and the connection portion in the planned formation position of the guard ring portion. It is also formed near the planned formation position. Therefore, even if the formation positions of the trenches 5a, 21a, and 30a are shifted due to the mask shift, the electric field relaxation layer 40 is accurately arranged at least in the guard ring portion where the electric field relaxation layer 40 is to be formed. You can make it. In addition, since the electric field relaxation layer 40 can be formed in a band-like frame shape, it can be easily formed without performing fine processing.

〔図３（ｄ）に示す工程〕
マスクを除去した後、ｐ型層を成膜したのち、ｐ型層のうちｎ+型ソース領域４の表面より上に形成された部分が取り除かれるようにエッチバックし、ｐ型ディープ層５、ｐ型ガードリング２１およびｐ型繋ぎ層３０を形成する。 [Step shown in FIG. 3D]
After removing the mask, a p-type layer is formed, and then the p-type layer is etched back so that a portion formed above the surface of the n + -type source region 4 is removed. The p-type guard ring 21 and the p-type connecting layer 30 are formed.

このとき、埋込エピにより、トレンチ５ａ、２１ａ、３０ａ内にｐ型層が埋め込まれることになるが、トレンチ５ａ、２１ａ、３０ａを同じ幅で形成していることから、ｐ型層の表面に形状異常が発生したり凹凸が発生することを抑制できる。したがって、各トレンチ５ａ、２１ａ、３０ａ内にｐ型層を確実に埋め込むことが可能になると共に、ｐ型層の表面は凹凸が少ない平坦な形状となる。   At this time, the p-type layer is buried in the trenches 5a, 21a, and 30a by the burying epi. However, since the trenches 5a, 21a, and 30a are formed with the same width, the p-type layer is formed on the surface of the p-type layer. It is possible to suppress the occurrence of shape abnormality and the occurrence of irregularities. Therefore, the p-type layer can be reliably embedded in each of the trenches 5a, 21a, and 30a, and the surface of the p-type layer has a flat shape with little unevenness.

また、エッチバック時には、ｐ型層の表面が凹凸の少ない平坦な形状となっていることから、ｐ型ディープ層５、ｐ型ガードリング２１およびｐ型繋ぎ層３０の表面は平坦な状態となる。したがって、この後にトレンチゲート構造を形成するための各種プロセスを行ったときに、所望のゲート形状を得ることが可能となる。また、各トレンチ５ａ、２１ａ、３０ａ内にｐ型層が確実に埋め込まれているため、ｐ型繋ぎ層３０の厚みが薄くなる等の問題も発生しない。   In addition, since the surface of the p-type layer has a flat shape with little unevenness at the time of the etch back, the surfaces of the p-type deep layer 5, the p-type guard ring 21, and the p-type connecting layer 30 are flat. . Therefore, when various processes for forming a trench gate structure are performed thereafter, a desired gate shape can be obtained. In addition, since the p-type layers are securely buried in the trenches 5a, 21a, and 30a, problems such as a reduction in the thickness of the p-type connecting layer 30 do not occur.

〔図４（ａ）に示す工程〕
ｎ+型ソース領域４などの上に図示しないマスクを形成したのち、マスクのうちのゲートトレンチ６の形成予定領域を開口させる。そして、マスクを用いてＲＩＥなどの異方性エッチングを行うことで、ゲートトレンチ６を形成する。 [Step shown in FIG. 4 (a)]
After forming a mask (not shown) on the n + -type source region 4 and the like, a region of the mask where the gate trench 6 is to be formed is opened. Then, a gate trench 6 is formed by performing anisotropic etching such as RIE using a mask.

さらに、マスクを除去したのち、再び図示しないマスクを形成し、マスクのうちの凹部２０の形成予定領域を開口させる。そして、マスクを用いてＲＩＥなどの異方性エッチングを行うことで凹部２０を形成する。これにより、凹部２０が形成された位置において、ｎ+型ソース領域４およびｐ型ベース領域３を貫通してｎ型電流分散層２ａが露出させられ、ｎ型電流分散層２ａの表面から複数本のｐ型ガードリング２１が配置された構造が構成される。 Further, after removing the mask, a mask (not shown) is formed again, and a region where the concave portion 20 is to be formed in the mask is opened. Then, the recess 20 is formed by performing anisotropic etching such as RIE using a mask. As a result, at the position where the concave portion 20 is formed, the n-type current spreading layer 2a is exposed through the n + -type source region 4 and the p-type base region 3, and a plurality of n-type current spreading layers 2a Is constructed in which the p-type guard ring 21 is arranged.

なお、ここではゲートトレンチ６と凹部２０を別々のマスクを用いた別工程として形成したが、同じマスクを用いて同時に形成することもできる。   Here, the gate trench 6 and the concave portion 20 are formed as separate steps using different masks, but they can be formed simultaneously using the same mask.

〔図４（ｂ）に示す工程〕
マスクを除去した後、例えば熱酸化を行うことによって、ゲート絶縁膜７を形成し、ゲート絶縁膜７によってゲートトレンチ６の内壁面上およびｎ+型ソース領域４の表面上を覆う。そして、ｐ型不純物もしくはｎ型不純物がドープされたＰｏｌｙ−Ｓｉをデポジションした後、これをエッチバックし、少なくともゲートトレンチ６内にＰｏｌｙ−Ｓｉを残すことでゲート電極８を形成する。 [Step shown in FIG. 4B]
After removing the mask, a gate insulating film 7 is formed, for example, by performing thermal oxidation, and covers the inner wall surface of the gate trench 6 and the surface of the n + -type source region 4 with the gate insulating film 7. After depositing Poly-Si doped with a p-type impurity or an n-type impurity, this is etched back, and at least the Poly-Si is left in the gate trench 6 to form the gate electrode 8.

〔図４（ｃ）に示す工程〕
ゲート電極８およびゲート絶縁膜７の表面を覆うように、例えば酸化膜などによって構成される層間絶縁膜１０を形成する。そして、層間絶縁膜１０の表面上に図示しないマスクを形成したのち、マスクのうち各ゲート電極８の間に位置する部分、つまりｐ型ディープ層５と対応する部分およびその近傍を開口させる。この後、マスクを用いて層間絶縁膜１０をパターニングすることでｐ型ディープ層５およびｎ+型ソース領域４を露出させるコンタクトホールを形成する。 [Step shown in FIG. 4 (c)]
An interlayer insulating film 10 made of, for example, an oxide film is formed so as to cover the surfaces of the gate electrode 8 and the gate insulating film 7. Then, after forming a mask (not shown) on the surface of the interlayer insulating film 10, a portion of the mask located between the gate electrodes 8, that is, a portion corresponding to the p-type deep layer 5 and its vicinity is opened. Thereafter, a contact hole exposing the p-type deep layer 5 and the n + -type source region 4 is formed by patterning the interlayer insulating film 10 using a mask.

〔図４（ｄ）に示す工程〕
層間絶縁膜１０の表面上に例えば複数の金属の積層構造により構成される電極材料を形成する。そして、電極材料をパターニングすることで、ソース電極９およびゲートパッド３１を形成する。なお、本図とは異なる断面において各セルのゲート電極８に繋がるゲート引出部が設けられている。その引出部において層間絶縁膜１０にコンタクトホールが開けられることで、ゲートパッド３１とゲート電極８との電気的接続が行われるようになっている。 [Step shown in FIG. 4D]
On the surface of the interlayer insulating film 10, for example, an electrode material having a laminated structure of a plurality of metals is formed. Then, the source electrode 9 and the gate pad 31 are formed by patterning the electrode material. It is to be noted that a gate lead portion connected to the gate electrode 8 of each cell is provided in a cross section different from that of this drawing. By forming a contact hole in the interlayer insulating film 10 at the leading portion, electrical connection between the gate pad 31 and the gate electrode 8 is established.

この後の工程については図示しないが、ｎ+型基板１の裏面側にドレイン電極１１を形成するなどの工程を行うことで、本実施形態にかかるＳｉＣ半導体装置が完成する。 Although the subsequent steps are not shown, the SiC semiconductor device according to the present embodiment is completed by performing steps such as forming the drain electrode 11 on the back surface side of the n + type substrate 1.

以上説明したように、本実施形態では、繋ぎ部からガードリング部に至るようにｎ-型ドリフト層２の表層部に、電界緩和用の電界緩和層４０を形成している。このため、ｐ型ガードリング２１の間への電界の入り込みを抑制することができる。これにより、電界集中が緩和され、電界集中による層間絶縁膜１０の破壊が抑制されて、耐圧低下を抑制することが可能となる。したがって、所望の耐圧を得ることが可能なＳｉＣ半導体装置とすることができる。 As described above, in the present embodiment, the electric field relaxation layer 40 for electric field relaxation is formed on the surface layer of the n − -type drift layer 2 from the connection portion to the guard ring portion. Therefore, it is possible to suppress an electric field from entering between the p-type guard rings 21. This alleviates the electric field concentration, suppresses the destruction of the interlayer insulating film 10 due to the electric field concentration, and suppresses the reduction in breakdown voltage. Therefore, a SiC semiconductor device capable of obtaining a desired breakdown voltage can be obtained.

（第２実施形態）
第２実施形態について説明する。本実施形態は、第１実施形態に対して電界緩和層４０の上面レイアウトを変更したものであり、その他については第１実施形態と同様であるため、第１実施形態と異なる部分についてのみ説明する。 (2nd Embodiment)
A second embodiment will be described. In the present embodiment, the layout of the upper surface of the electric field relaxation layer 40 is changed from that of the first embodiment, and the other parts are the same as those of the first embodiment. Therefore, only the parts different from the first embodiment will be described. .

図５に示すように、本実施形態では、電界緩和層４０を複数本のライン状としている。より詳しくは、電界緩和層４０は、四隅が丸められた四角形状のｐ型ガードリング２１のうちの各辺と対応する位置では、等間隔に当該各辺に対する法線方向に延設されており、四隅と対応する位置ではｐ型ガードリング２１の中心から放射方向に延設されている。すなわち、電界緩和層４０をｐ型ガードリング２１に対して直交配置している。   As shown in FIG. 5, in this embodiment, the electric field relaxation layer 40 has a plurality of lines. More specifically, the electric field relaxation layer 40 extends at regular intervals in the normal direction to each side at a position corresponding to each side of the square p-type guard ring 21 whose four corners are rounded. At the positions corresponding to the four corners, the p-type guard ring 21 extends radially from the center. That is, the electric field relaxation layer 40 is arranged orthogonal to the p-type guard ring 21.

このように、電界緩和層４０をｐ型ガードリング２１に対して直交配置するようにしても、第１実施形態と同様の効果を得ることができる。   Thus, even if the electric field relaxation layer 40 is arranged orthogonal to the p-type guard ring 21, the same effect as in the first embodiment can be obtained.

また、第１実施形態と比較して電界緩和層４０の形成面積が小さくなるため、最小限のｐ型不純物ドーズによって効果的に電界緩和が行えると共に、イオン注入欠陥による高電圧印加時のリークを最小限に抑えることが可能となる。   Further, since the formation area of the electric field relaxation layer 40 is smaller than that of the first embodiment, the electric field can be effectively alleviated with a minimum p-type impurity dose, and the leakage at the time of applying a high voltage due to ion implantation defects can be reduced. It can be minimized.

（第３実施形態）
第３実施形態について説明する。本実施形態は、第１、第２実施形態で説明した電界緩和層４０の代わりとなる不純物層を備えるようにしたものであり、その他については第１、第２実施形態と同様であるため、第１、第２実施形態と異なる部分についてのみ説明する。 (Third embodiment)
A third embodiment will be described. The present embodiment is provided with an impurity layer that replaces the electric field relaxation layer 40 described in the first and second embodiments, and is otherwise the same as the first and second embodiments. Only parts different from the first and second embodiments will be described.

図６に示すように、本実施形態では、電界緩和層４０の代わりに、ガードリング部内におけるｎ型電流分散層２ａ内に、電界緩和層５０を形成している。   As shown in FIG. 6, in the present embodiment, instead of the electric field relaxation layer 40, the electric field relaxation layer 50 is formed in the n-type current distribution layer 2a in the guard ring portion.

本実施形態では、電界緩和層５０は、ガードリング部の全域に形成されている。より詳しくは、電界緩和層５０は、ガードリング部において、枠体形状に形成されている。電界緩和層５０は、ｎ型電流分散層２ａよりもキャリア濃度が低くされたｎ型層、もしくは、ｐ型ガードリング２１よりもキャリア濃度が低くされたｐ型層で構成されている。すなわち、電界緩和層５０内におけるドナー濃度Ｎｄとアクセプタ濃度Ｎａとの差の絶対値が、ｎ型電流分散層２ａやｐ型ガードリング２１のキャリア濃度よりも低くされており、例えば｜Ｎｄ−Ｎａ｜＜０．５×１０17／ｃｍ3とされている。電界緩和層５０の厚みについては任意であり、例えば０．５μｍ程度とされる。 In the present embodiment, the electric field relaxation layer 50 is formed over the entire area of the guard ring portion. More specifically, the electric field relaxation layer 50 is formed in a frame shape at the guard ring portion. The electric field relaxation layer 50 is formed of an n-type layer having a lower carrier concentration than the n-type current dispersion layer 2 a or a p-type layer having a lower carrier concentration than the p-type guard ring 21. That is, the absolute value of the difference between the donor concentration Nd and the acceptor concentration Na in the electric field relaxation layer 50 is set lower than the carrier concentration of the n-type current dispersion layer 2a or the p-type guard ring 21, and | Nd-Na | <0.5 × 10 17 / cm 3 . The thickness of the electric field relaxation layer 50 is arbitrary, and is, for example, about 0.5 μm.

また、本実施形態では、電界緩和層５０を、ｐ型ガードリング２１の厚み内、つまりｐ型ガードリング２１のうちの層間絶縁膜１０側となる表面からｎ-型ドリフト層２側となる底面までの間に形成してある。ただし、電界緩和層５０の形成深さについては、電界緩和層５０のうちの層間絶縁膜１０側となる上面側がｐ型ガードリング２１の表面よりも深く、かつ、底面よりも浅い位置となっていれば良い。つまり、電界緩和層５０のうちのｎ-型ドリフト層２側となる下面側については、ｐ型ガードリング２１の底面よりも深い位置となっていても良い。 In the present embodiment, the electric field relaxation layer 50 is formed within the thickness of the p-type guard ring 21, that is, the bottom surface of the p-type guard ring 21 from the surface on the side of the interlayer insulating film 10 to the side of the n − -type drift layer 2. It is formed before. However, regarding the formation depth of the electric field relaxation layer 50, the upper surface side of the electric field relaxation layer 50 which is closer to the interlayer insulating film 10 is located deeper than the surface of the p-type guard ring 21 and shallower than the bottom surface. Just do it. That is, the lower surface side of the electric field relaxation layer 50 that is the n − -type drift layer 2 side may be located deeper than the bottom surface of the p-type guard ring 21.

このように、ガードリング部においてｎ型電流分散層２ａ内に電界緩和層５０を形成するようにしている。このような電界緩和層５０を形成しても、ｐ型ガードリング２１間への電界の入り込みを抑制することができる。したがって、第１、第２実施形態と同様の効果を得ることができる。   As described above, the electric field relaxation layer 50 is formed in the n-type current distribution layer 2a in the guard ring portion. Even if such an electric field relaxation layer 50 is formed, it is possible to suppress the electric field from entering between the p-type guard rings 21. Therefore, the same effects as in the first and second embodiments can be obtained.

次に、本実施形態のＳｉＣ半導体装置の製造方法について説明する。なお、本実施形態のＳｉＣ半導体装置の製造方法については、ほぼ第１実施形態で説明した図３および図４に示すＳｉＣ半導体装置の製造方法と同様であるため、異なる部分を主に説明する。   Next, a method for manufacturing the SiC semiconductor device of the present embodiment will be described. Note that the method of manufacturing the SiC semiconductor device of the present embodiment is almost the same as the method of manufacturing the SiC semiconductor device shown in FIGS. 3 and 4 described in the first embodiment, and therefore different portions will be mainly described.

〔図７（ａ）に示す工程〕
まず、ｎ+型基板１の主表面上にＳｉＣからなるｎ-型ドリフト層２、ｎ型電流分散層２ａ、ｐ型ベース領域３およびｎ+型ソース領域４を順にエピタキシャル成長させる。 [Step shown in FIG. 7A]
First, an n − -type drift layer 2 made of SiC, an n-type current spreading layer 2a, a p-type base region 3 and an n + -type source region 4 are epitaxially grown on the main surface of an n + -type substrate 1 in this order.

〔図７（ｂ）に示す工程〕
次に、図３（ｃ）、（ｄ）に示す工程と同様の工程を行うことで、トレンチ５ａ、２１ａ、３０ａを形成すると共に、トレンチ５ａ、２１ａ、３０ａ内にｐ型ディープ層５、ｐ型ガードリング２１およびｐ型繋ぎ層３０を形成する。 [Step shown in FIG. 7B]
Next, by performing the same steps as those shown in FIGS. 3C and 3D, the trenches 5a, 21a and 30a are formed, and the p-type deep layers 5 and p are formed in the trenches 5a, 21a and 30a. The mold guard ring 21 and the p-type connecting layer 30 are formed.

〔図７（ｃ）に示す工程〕
図示しないマスクを形成し、マスクのうちの凹部２０の形成予定領域を開口させる。そして、マスクを用いてＲＩＥなどの異方性エッチングを行うことで凹部２０を形成する。これにより、凹部２０が形成された位置において、ｎ+型ソース領域４およびｐ型ベース領域３を貫通してｎ型電流分散層２ａが露出させられ、ｎ型電流分散層２ａの表層部に複数本のｐ型ガードリング２１が配置された構造が構成される。 [Step shown in FIG. 7C]
A mask (not shown) is formed, and a region where the concave portion 20 is to be formed in the mask is opened. Then, the recess 20 is formed by performing anisotropic etching such as RIE using a mask. As a result, at the position where the concave portion 20 is formed, the n-type current spreading layer 2a is exposed through the n + -type source region 4 and the p-type base region 3, and a plurality of A structure in which the p-type guard rings 21 are arranged is configured.

さらに、凹部２０の形成時に用いたマスクをそのまま用いて、ｎ型不純物をイオン注入したのち、活性化アニールを行うことで、凹部２０内に電界緩和層５０を形成する。このときのｎ型不純物のドーズ量については、上記したように、電界緩和層５０のドナー濃度Ｎｄとアクセプタ濃度Ｎａとの差の絶対値について、｜Ｎｄ−Ｎａ｜＜０．５×１０１７／ｃｍ３が成り立つように調整している。この後、凹部２０の形成や電界緩和層５０の形成時に用いたマスクを除去したのち、図３（ｄ）に示す工程のうちのゲートトレンチ６の形成工程を行う。 Further, an n-type impurity is ion-implanted using the mask used for forming the recess 20 as it is, and then activation annealing is performed to form the electric field relaxation layer 50 in the recess 20. At this time, as for the dose of the n-type impurity, as described above, regarding the absolute value of the difference between the donor concentration Nd and the acceptor concentration Na of the electric field relaxation layer 50, | Nd−Na | <0.5 × 10 17 / It is adjusted so that cm 3 holds. Then, after removing the mask used for forming the concave portion 20 and the electric field relaxation layer 50, the gate trench 6 forming step of the step shown in FIG. 3D is performed.

〔図７（ｄ）に示す工程〕
更に図４（ａ）以降の各工程を行う。これにより、本実施形態のＳｉＣ半導体装置を製造することができる。 [Step shown in FIG. 7D]
Further performing the steps of FIGS. 4 (a) later. Thereby, the SiC semiconductor device of the present embodiment can be manufactured.

（第３実施形態の変形例）
上記第３実施形態で説明した電界緩和層５０をガードリング部の全域に形成する必要はなく、例えば図８に示すように、ガードリング部のうちのセル部や繋ぎ部寄りの位置にのみ形成していても良い。さらに、電界緩和層５０が繋ぎ部のうちのガードリング部寄りの位置にまで形成してあっても良い。 (Modification of Third Embodiment)
It is not necessary to form the electric field relaxation layer 50 described in the third embodiment over the entire area of the guard ring part. For example, as shown in FIG. 8, the electric field relaxation layer 50 is formed only at a position near the cell part or the joint part in the guard ring part. May be. Further, the electric field relaxation layer 50 may be formed up to a position near the guard ring part in the connection part.

ただし、これらの構造とする場合には、凹部２０を形成する際に用いたマスクとは別のマスク、例えばレジストマスクを用いて、電界緩和層５０を形成するためのイオン注入を行うことが必要になる。   However, in the case of using these structures, it is necessary to perform ion implantation for forming the electric field relaxation layer 50 using a mask different from the mask used when forming the concave portion 20, for example, a resist mask. become.

なお、電界緩和層５０をガードリング部のうちのセル部や繋ぎ部寄りの位置にのみ形成する場合、電界緩和層５０の罫線範囲については、ｐ型ガードリング２１の配置間隔やｐ型ガードリング２１とｎ型電流分散層２ａそれぞれの不純物濃度に基づいて決めている。上記したように、ｐ型ガードリング２１は、セル部側において電界集中を緩和して等電位線がより外周側に向かうように形成されるが、その配置間隔やｐ型ガードリング２１およびｎ型電流分散層２ａの不純物濃度によって電界の入り込み方が変わってくる。このため、仮に、電界緩和層５０が形成されていなければ、ｐ型ガードリング２１間への電界が入り込んだときに、その上に形成される層間絶縁膜１０まで達すると想定される位置を含むように、電界緩和層５０を形成している。   When the electric field relaxation layer 50 is formed only at a position near the cell portion or the connection portion of the guard ring portion, the arrangement interval of the p-type guard rings 21 and the p-type guard ring 21 and the n-type current dispersion layer 2a. As described above, the p-type guard ring 21 is formed so that the electric field concentration is reduced on the cell portion side so that the equipotential lines are directed to the outer peripheral side. The manner in which the electric field enters depends on the impurity concentration of the current dispersion layer 2a. For this reason, if the electric field relaxation layer 50 is not formed, when an electric field enters between the p-type guard rings 21, it includes a position that is assumed to reach the interlayer insulating film 10 formed thereon. Thus, the electric field relaxation layer 50 is formed.

（他の実施形態）
本発明は上記した実施形態に限定されるものではなく、特許請求の範囲に記載した範囲内において適宜変更が可能である。 (Other embodiments)
The present invention is not limited to the embodiments described above, and can be appropriately modified within the scope described in the claims.

（１）上記各実施形態では、ｐ型ベース領域３の上にｎ+型ソース領域４を連続してエピタキシャル成長させて形成したが、ｐ型ベース領域３の所望位置にｎ型不純物をイオン注入することでｎ+型ソース領域４を形成しても良い。 (1) In each of the above embodiments, the n + -type source region 4 is formed by continuous epitaxial growth on the p-type base region 3, but an n-type impurity is ion-implanted into a desired position of the p-type base region 3. Thus, the n + type source region 4 may be formed.

（２）上記各実施形態では、縦型のパワー素子としてｎチャネルタイプの反転型のトレンチゲート構造のＭＯＳＦＥＴを例に挙げて説明した。しかしながら、上記各実施形態は縦型の半導体素子の一例を示したに過ぎず、半導体基板の表面側に設けられる第１電極と裏面側に設けられる第２電極との間に電流を流す縦型の半導体素子であれば、他の構造もしくは導電型のものであっても良い。   (2) In each of the above embodiments, an n-channel inversion type MOSFET having a trench gate structure has been described as an example of a vertical power element. However, each of the above embodiments is merely an example of a vertical semiconductor device, and a vertical semiconductor device in which a current flows between a first electrode provided on the front surface side of a semiconductor substrate and a second electrode provided on the back surface side. The semiconductor element may have another structure or conductivity type.

例えば、上記第１実施形態等では、第１導電型をｎ型、第２導電型をｐ型としたｎチャネルタイプのＭＯＳＦＥＴを例に挙げて説明したが、各構成要素の導電型を反転させたｐチャネルタイプのＭＯＳＦＥＴとしても良い。また、上記説明では、半導体素子としてＭＯＳＦＥＴを例に挙げて説明したが、同様の構造のＩＧＢＴに対しても本発明を適用することができる。ＩＧＢＴは、上記各実施形態に対してｎ+型基板１の導電型をｎ型からｐ型に変更するだけであり、その他の構造や製造方法に関しては上記各実施形態と同様である。さらに、縦型のＭＯＳＦＥＴとしてトレンチゲート構造のものを例に挙げて説明したが、トレンチゲート構造のものに限らず、プレーナ型のものであっても良い。 For example, in the first embodiment and the like, an n-channel MOSFET in which the first conductivity type is n-type and the second conductivity type is p-type has been described as an example, but the conductivity type of each component is reversed. Alternatively, a p-channel type MOSFET may be used. In the above description, the MOSFET has been described as an example of the semiconductor element. However, the present invention can be applied to an IGBT having a similar structure. The IGBT differs from the above embodiments only in that the conductivity type of the n + type substrate 1 is changed from n type to p type, and the other structures and manufacturing methods are the same as in the above embodiments. Furthermore, although the vertical MOSFET has a trench gate structure as an example, the MOSFET is not limited to the trench gate structure but may be a planar MOSFET.

さらに、ＭＯＳ構造のパワー素子に限らず、ショットキーダイオードを適用することもできる。具体的には、ｎ+型基板の主表面上にｎ-型ドリフト層が形成されていると共に、その上に第１電極に相当するショットキー電極が形成され、さらにｎ+型基板の裏面側に第２電極に相当するオーミック電極が形成されることでショットキーダイオードが構成される。このような構造において、ｎ-型ドリフト層の表層部から複数本のｐ型ディープ層が形成されることで、ジャンクションバリアショットキーダイオード（以下、ＪＢＳという）が構成される。このようなＪＢＳが備えられるＳｉＣ半導体装置においても、第１、第２実施形態で説明した電界緩和層４０や第３実施形態で説明した電界緩和層５０を備えることで、上記各実施形態と同様の効果を得ることができる。 Further, a Schottky diode can be applied without being limited to a power element having a MOS structure. Specifically, an n − -type drift layer is formed on the main surface of the n + -type substrate, a Schottky electrode corresponding to the first electrode is formed thereon, and further, a back side of the n + -type substrate is formed. The Schottky diode is formed by forming an ohmic electrode corresponding to the second electrode. In such a structure, a junction barrier Schottky diode (hereinafter, referred to as JBS) is formed by forming a plurality of p-type deep layers from the surface of the n − -type drift layer. Also in the SiC semiconductor device provided with such a JBS, the electric field relaxation layer 40 described in the first and second embodiments and the electric field relaxation layer 50 described in the third embodiment are provided, so that the same as each of the above embodiments is provided. The effect of can be obtained.

（３）上記各実施形態では、ｐ型ディープ層５やｐ型ガードリング２１およびｐ型繋ぎ層３０を埋込エピ成長によって形成したが、イオン注入によって形成しても良い。   (3) In each of the above embodiments, the p-type deep layer 5, the p-type guard ring 21, and the p-type connecting layer 30 are formed by buried epi growth, but may be formed by ion implantation.

（４）上記各実施形態では、ｐ型ディープ層５やｐ型繋ぎ層３０をｎ+型ソース領域４およびｐ型ベース領域３を貫通するように形成しているが、ｐ型ベース領域３の下方にのみｐ型ディープ層５やｐ型繋ぎ層３０を形成するようにしても良い。 (4) In each of the above embodiments, the p-type deep layer 5 and the p-type connecting layer 30 are formed so as to penetrate the n + -type source region 4 and the p-type base region 3. The p-type deep layer 5 and the p-type connecting layer 30 may be formed only below.

（５）なお、結晶の方位を示す場合、本来ならば所望の数字の上にバー（−）を付すべきであるが、電子出願に基づく表現上の制限が存在するため、本明細書においては、所望の数字の前にバーを付すものとする。   (5) When indicating the orientation of a crystal, a bar (-) should normally be added to a desired number. However, since there are restrictions on the expression based on the electronic application, in this specification, , A bar before the desired number.

１ ｎ+型基板
２ａ ｎ型電流分散層
３ ｐ型ベース領域
４ ｎ+型ソース領域
５ ｐ型ディープ層
８ ゲート電極
９ ソース電極
１１ ドレイン電極
２１ ｐ型ガードリング層
４０、５０ 電界緩和層 Reference Signs List 1 n + type substrate 2 a n type current spreading layer 3 p type base region 4 n + type source region 5 p type deep layer 8 gate electrode 9 source electrode 11 drain electrode 21 p type guard ring layer 40, 50 electric field relaxation layer

Claims (9)

セル部と前記セル部の外周を囲むガードリング部を含む外周部を有する炭化珪素半導体装置であって、
前記セル部および前記外周部には、
第１または第２導電型の基板（１）と、
前記基板の表面側に形成され、前記基板よりも低不純物濃度とされた第１導電型のドリフト層（２）と、
前記ドリフト層の上に形成され、前記ドリフト層よりも高不純物濃度とされた第１導電型の電流分散層（２ａ）と、が備えられ、
前記セル部には、
前記電流分散層にストライプ状に形成された第２導電型層（５）と、
前記第２導電型層に電気的に接続された第１電極（９）と、
前記基板の裏面側に電気的に接続された第２電極（１１）と、を有し、
前記第１電極と前記第２電極との間に電流を流す縦型の半導体素子が備えられ、
前記ガードリング部には、
前記電流分散層の表面から形成されていると共に前記セル部を囲む複数の枠形状とされたライン状の第２導電型のガードリング（２１）が備えられ、
前記ガードリング部において前記セル部よりも前記電流分散層が凹んだ凹部（２０）が形成されることで、前記基板の厚み方向において、前記セル部が前記ガードリング部よりも突き出した島状のメサ部が構成され、
前記メサ部と前記凹部との境界位置から前記メサ部の外周側に向けて、前記ドリフト層の表層部に、前記ガードリングよりも低不純物濃度とされた第２導電型の電界緩和層（４０）が備えられている炭化珪素半導体装置。 A silicon carbide semiconductor device having a cell portion and an outer peripheral portion including a guard ring portion surrounding the outer periphery of the cell portion,
In the cell portion and the outer peripheral portion,
A first or second conductivity type substrate (1);
A first conductivity type drift layer (2) formed on the surface side of the substrate and having a lower impurity concentration than the substrate;
A first conductivity type current spreading layer (2a) formed on the drift layer and having a higher impurity concentration than the drift layer;
In the cell part,
A second conductivity type layer (5) formed in a stripe shape on the current distribution layer;
A first electrode (9) electrically connected to the second conductivity type layer;
A second electrode (11) electrically connected to the back side of the substrate;
A vertical semiconductor element for flowing a current between the first electrode and the second electrode;
In the guard ring portion,
A plurality of frame-shaped line-shaped second conductivity type guard rings (21) formed from the surface of the current distribution layer and surrounding the cell portion;
By forming a concave portion (20) in which the current distribution layer is recessed from the cell portion in the guard ring portion, an island-like shape in which the cell portion protrudes from the guard ring portion in the thickness direction of the substrate. The mesa section is configured,
From a boundary position between the mesa portion and the concave portion toward the outer peripheral side of the mesa portion, a second conductivity type electric field relaxation layer (40) having a lower impurity concentration than the guard ring is formed on the surface layer portion of the drift layer. ) Is provided. 前記電界緩和層は、前記メサ部を囲む帯状の枠体形状とされている請求項１に記載の炭化珪素半導体装置。   The silicon carbide semiconductor device according to claim 1, wherein the electric field relaxation layer has a band-like frame shape surrounding the mesa portion. 前記電界緩和層は、前記ガードリングに対して直交配置された複数本のライン状とされている請求項１に記載の炭化珪素半導体装置。   2. The silicon carbide semiconductor device according to claim 1, wherein the electric field relaxation layer has a plurality of lines arranged orthogonal to the guard ring. 3. セル部と前記セル部の外周を囲むガードリング部を含む外周部を有する炭化珪素半導体装置であって、
前記セル部および前記外周部には、
第１または第２導電型の基板（１）と、
前記基板の表面側に形成され、前記基板よりも低不純物濃度とされた第１導電型のドリフト層（２）と、
前記ドリフト層の上に形成され、前記ドリフト層よりも高不純物濃度とされた第１導電型の電流分散層（２ａ）と、が備えられ、
前記セル部には、
前記電流分散層にストライプ状に形成された第２導電型層（５）と、
前記第２導電型層に電気的に接続された第１電極（９）と、
前記基板の裏面側に電気的に接続された第２電極（１１）と、を有し、
前記第１電極と前記第２電極との間に電流を流す縦型の半導体素子が備えられ、
前記ガードリング部には、
前記電流分散層の表面から形成されていると共に前記セル部を囲む複数の枠形状とされたライン状の第２導電型のガードリング（２１）が備えられ、
前記ガードリング部において前記セル部よりも前記電流分散層が凹んだ凹部（２０）が形成されることで、前記基板の厚み方向において、前記セル部が前記ガードリング部よりも突き出した島状のメサ部が構成され、
前記メサ部と前記凹部との境界位置から前記メサ部の外周側に向けて、前記電流分散層内に、前記電流分散層および前記ガードリングよりもキャリア濃度が低くされた第１導電型または第２導電型の電界緩和層（５０）が備えられ、
前記電界緩和層の上面は、前記ガードリングの表面よりも深く、かつ、底面よりも浅い位置とされている炭化珪素半導体装置。 A silicon carbide semiconductor device having a cell portion and an outer peripheral portion including a guard ring portion surrounding the outer periphery of the cell portion,
In the cell portion and the outer peripheral portion,
A first or second conductivity type substrate (1);
A first conductivity type drift layer (2) formed on the surface side of the substrate and having a lower impurity concentration than the substrate;
A first conductivity type current spreading layer (2a) formed on the drift layer and having a higher impurity concentration than the drift layer;
In the cell part,
A second conductivity type layer (5) formed in a stripe shape on the current distribution layer;
A first electrode (9) electrically connected to the second conductivity type layer;
A second electrode (11) electrically connected to the back side of the substrate;
A vertical semiconductor element for flowing a current between the first electrode and the second electrode;
In the guard ring portion,
A plurality of frame-shaped line-shaped second conductivity type guard rings (21) formed from the surface of the current distribution layer and surrounding the cell portion;
By forming a concave portion (20) in which the current distribution layer is recessed from the cell portion in the guard ring portion, an island-like shape in which the cell portion protrudes from the guard ring portion in the thickness direction of the substrate. The mesa section is configured,
From the boundary position between the mesa portion and the concave portion toward the outer peripheral side of the mesa portion, the first conductivity type or the first conductivity type in which the carrier concentration is lower than the current dispersion layer and the guard ring in the current dispersion layer. second conductivity type field relaxation layer (50) is provided with al will,
A silicon carbide semiconductor device in which an upper surface of the electric field relaxation layer is deeper than a surface of the guard ring and shallower than a bottom surface . 前記電界緩和層は、前記ガードリング部の全域に形成されている請求項４に記載の炭化珪素半導体装置。   5. The silicon carbide semiconductor device according to claim 4, wherein said electric field relaxation layer is formed in an entire area of said guard ring portion. 前記セル部には、
前記電流分散層の上に形成された第２導電型のベース領域（３）と、
前記ベース領域の上に形成され、前記ドリフト層よりも高不純物濃度とされた第１導電型のソース領域（４）と、
前記ソース領域の表面から前記ベース領域よりも深くまで形成されたゲートトレンチ（６）内に形成され、該ゲートトレンチの内壁面に形成されたゲート絶縁膜（７）と、前記ゲート絶縁膜の上に形成されたゲート電極（８）と、を有して構成されたトレンチゲート構造と、
前記ゲートトレンチよりも深い位置まで形成されたトレンチ（５ａ）内に配置された前記第２導電型層と、
前記ソース領域および前記ベース領域に電気的に接続された前記第１電極を構成するソース電極（９）と、
前記基板の裏面側に電気的に接続された前記第２電極を構成するドレイン電極（１１）と、を備えた縦型の半導体素子が形成されている請求項１ないし５のいずれか１つに記載の炭化珪素半導体装置。 In the cell part,
A second conductivity type base region (3) formed on the current distribution layer;
A first conductivity type source region (4) formed on the base region and having a higher impurity concentration than the drift layer;
A gate insulating film (7) formed in a gate trench (6) formed from the surface of the source region to a depth deeper than the base region, and formed on an inner wall surface of the gate trench; A gate electrode (8) formed in the trench gate structure,
The second conductivity type layer disposed in a trench (5a) formed to a position deeper than the gate trench;
A source electrode (9) constituting the first electrode electrically connected to the source region and the base region;
A drain electrode (11) constituting an electrically connected to said second electrode on the back side of the substrate, to to any one of 5 claims 1 vertical semiconductor device is formed with a The silicon carbide semiconductor device according to the above. セル部と前記セル部の外周を囲むガードリング部を含む外周部を有する炭化珪素半導体装置の製造方法であって、
第１または第２導電型の基板（１）を用意することと、
前記基板の表面側に、前記基板よりも低不純物濃度とされた第１導電型のドリフト層（２）を形成することと、
前記ドリフト層の表層部に、第２導電型不純物をイオン注入することで第２導電型の電界緩和層（４０）を形成することと、
前記ドリフト層の上に、前記ドリフト層よりも高不純物濃度とされた第１導電型の電流分散層（２ａ）を形成することと、
前記セル部において、前記電流分散層にストライプ状に第２導電型層（５）を形成すると共に、前記ガードリング部において、前記電流分散層に前記セル部を囲む複数の枠形状とされるライン状の第２導電型のガードリング（２１）を形成することと、
前記ガードリング部において、前記セル部よりも前記電流分散層を凹ませた凹部（２０）を形成することで、前記基板の厚み方向において、前記セル部が前記ガードリング部よりも突き出した島状のメサ部を構成することと、
前記第２導電型層に電気的に接続される第１電極（９）を形成することと、
前記基板の裏面側に電気的に接続される第２電極（１１）を形成することと、を含み、
前記電界緩和層を形成することでは、前記メサ部と前記凹部との境界位置となる予定の位置から前記メサ部の外周側に向けて前記電界緩和層を形成する炭化珪素半導体装置の製造方法。 A method for manufacturing a silicon carbide semiconductor device having a cell portion and an outer peripheral portion including a guard ring portion surrounding the outer periphery of the cell portion,
Providing a first or second conductivity type substrate (1);
Forming a first conductivity type drift layer (2) having a lower impurity concentration than the substrate on the surface side of the substrate;
Forming a second conductivity type electric field relaxation layer (40) by ion-implanting a second conductivity type impurity into a surface portion of the drift layer;
Forming a first conductivity type current dispersion layer (2a) having a higher impurity concentration than the drift layer on the drift layer;
In the cell portion, a second conductive type layer (5) is formed in a stripe shape on the current distribution layer, and in the guard ring portion, the current distribution layer has a plurality of frame-shaped lines surrounding the cell portion. Forming a second guard ring (21) of a second conductivity type;
By forming a recess (20) in which the current distribution layer is recessed from the cell portion in the guard ring portion, an island shape in which the cell portion protrudes from the guard ring portion in the thickness direction of the substrate. The mesa section of the
Forming a first electrode (9) electrically connected to the second conductivity type layer;
Forming a second electrode (11) that is electrically connected to the back side of the substrate;
The method for manufacturing a silicon carbide semiconductor device, wherein the forming of the electric field relaxation layer includes forming the electric field relaxation layer from a position to be a boundary position between the mesa portion and the concave portion toward an outer peripheral side of the mesa portion. セル部と前記セル部の外周を囲むガードリング部を含む外周部を有する炭化珪素半導体装置の製造方法であって、
第１または第２導電型の基板（１）を用意することと、
前記基板の表面側に、前記基板よりも低不純物濃度とされた第１導電型のドリフト層（２）を形成することと、
前記ドリフト層の上に、前記ドリフト層よりも高不純物濃度とされた第１導電型の電流分散層（２ａ）を形成することと、
前記電流分散層内に、第２導電型不純物をイオン注入することで第１導電型または第２導電型の電界緩和層（５０）を形成することと、
前記セル部において、前記電流分散層にストライプ状に第２導電型層（５）を形成すると共に、前記ガードリング部において、前記電流分散層に前記セル部を囲む複数の枠形状とされるライン状の第２導電型のガードリング（２１）を形成することと、
前記ガードリング部において、前記セル部よりも前記電流分散層を凹ませた凹部（２０）を形成することで、前記基板の厚み方向において、前記セル部が前記ガードリング部よりも突き出した島状のメサ部を構成することと、
前記第２導電型層に電気的に接続される第１電極（９）を形成することと、
前記基板の裏面側に電気的に接続される第２電極（１１）を形成することと、を含み、
前記電界緩和層を形成することでは、前記メサ部と前記凹部との境界位置となる予定の位置から前記メサ部の外周側に向けて、前記電流分散層および前記ガードリングよりもキャリア濃度が低くされた第１導電型もしくは第２導電型の前記電界緩和層を形成し、
さらに、前記電界緩和層を形成することでは、前記凹部を形成した後において、前記電界緩和層の上面が、前記ガードリングの表面よりも深く、かつ、底面よりも浅い位置とされるように前記電界緩和層を形成する炭化珪素半導体装置の製造方法。 A method for manufacturing a silicon carbide semiconductor device having a cell portion and an outer peripheral portion including a guard ring portion surrounding the outer periphery of the cell portion,
Providing a first or second conductivity type substrate (1);
Forming a first conductivity type drift layer (2) having a lower impurity concentration than the substrate on the surface side of the substrate;
Forming a first conductivity type current dispersion layer (2a) having a higher impurity concentration than the drift layer on the drift layer;
Forming a first conductivity type or second conductivity type electric field relaxation layer (50) by ion-implanting a second conductivity type impurity into the current dispersion layer;
In the cell portion, a second conductive type layer (5) is formed in a stripe shape on the current distribution layer, and in the guard ring portion, the current distribution layer has a plurality of frame-shaped lines surrounding the cell portion. Forming a second guard ring (21) of a second conductivity type;
By forming a recess (20) in which the current distribution layer is recessed from the cell portion in the guard ring portion, an island shape in which the cell portion protrudes from the guard ring portion in the thickness direction of the substrate. The mesa section of the
Forming a first electrode (9) electrically connected to the second conductivity type layer;
Forming a second electrode (11) that is electrically connected to the back side of the substrate;
By forming the electric field relaxation layer, the carrier concentration is lower than that of the current dispersion layer and the guard ring from a position to be a boundary position between the mesa portion and the concave portion toward the outer peripheral side of the mesa portion. Forming the electric field relaxation layer of the first conductivity type or the second conductivity type ,
Further, by forming the electric field relaxation layer, after forming the concave portion, the upper surface of the electric field relaxation layer is deeper than the surface of the guard ring, and is so positioned as to be shallower than the bottom surface. A method for manufacturing a silicon carbide semiconductor device in which an electric field relaxation layer is formed . 前記電流分散層の上に、第２導電型のベース領域（３）を形成することと、
前記ベース領域の上に、前記ドリフト層よりも高不純物濃度とされる第１導電型のソース領域（４）を形成することと、
前記ソース領域の表面から異方性エッチングを行うことで、前記セル部のディープトレンチ（５ａ）と、前記ガードリング部のガードリングトレンチ（２１ａ）と、を含むトレンチを形成することと、
第２導電型の炭化珪素層をエピタキシャル成長させることで、前記ディープトレンチおよび前記ガードリングトレンチを埋め込んだのち、エッチバックにより前記炭化珪素層のうち前記ソース領域の上に形成された部分を取り除くことで、前記ディープトレンチ内に前記第２導電型層を形成すると共に、前記ガードリングトレンチ内に前記ガードリングを形成することと、
前記セル部に、前記ソース領域の表面から前記ベース領域よりも深いゲートトレンチ（６）と、該ゲートトレンチの内壁面に形成されるゲート絶縁膜（７）と、前記ゲート絶縁膜の上に形成されるゲート電極（８）と、を有して構成されるトレンチゲート構造を形成することと、を含み、
前記第１電極を形成することでは、前記第１電極として、前記ソース領域および前記ベース領域に電気的に接続されるソース電極（９）を形成し、
前記第２電極を形成することでは、前記基板の裏面側に、前記第２電極としてドレイン電極（１１）を形成する請求項７または８に記載の炭化珪素半導体装置の製造方法。 Forming a second conductivity type base region (3) on the current distribution layer;
Forming a first conductivity type source region (4) having a higher impurity concentration than the drift layer on the base region;
Forming a trench including a deep trench (5a) in the cell portion and a guard ring trench (21a) in the guard ring portion by performing anisotropic etching from the surface of the source region;
After burying the deep trench and the guard ring trench by epitaxially growing a silicon carbide layer of the second conductivity type, a portion of the silicon carbide layer formed on the source region is removed by etch-back. Forming the second conductivity type layer in the deep trench and forming the guard ring in the guard ring trench;
A gate trench (6) deeper than the base region from the surface of the source region, a gate insulating film (7) formed on the inner wall surface of the gate trench, and a gate insulating film formed on the gate insulating film. Forming a trench gate structure configured with a gate electrode (8) to be formed.
In forming the first electrode, a source electrode (9) electrically connected to the source region and the base region is formed as the first electrode;
9. The method of manufacturing a silicon carbide semiconductor device according to claim 7 , wherein forming the second electrode forms a drain electrode as the second electrode on the back surface side of the substrate. 10.
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